1. Field of the Invention
The present Invention relates to a color liquid crystal display (LCD) system, and more particularly to illumination for liquid crystal display devices and field sequential color illumination for such devices in which said devices are illuminated by flashes of red, green, and blue light in sequence.
2. Prior Art
LCD technology has progressed rapidly in recent years. Most of the development effort has been directed toward TFT (thin film transistor) LCDs which have a transistor at each pixel. This allows one to regulate the amount of charge placed at the tiny capacitors located at each pixel, and thus precisely control the degree to which it turns on and off, in order to provide a gray scale. Such LCDs have very high contrast ratios, on the order of 100:1. The largest commercially available LCDs of this (or at the moment, any) type are about 15 inch (38 cm) on the diagonal. The highest resolutions available are about 640.times.480 pixels. The total numbers of colors that such LCDs can generate are in excess of 16 million with a suitable controller.
Although image quality of these LCDs is quite good in terms of contrast and color, their resolution and screen size make them suitable only for personal computer (PC) level applications. The industry is addressing both issues. The goal is the mass production of flat-panel LCD displays with at least the same quality as high-end cathode ray tube (CRT) displays.
Screen size is at present limited by the equipment required to manufacture the LCDs. The industry as a whole is introducing new systems that will allow the production of 14 inch (35 cm) and larger TFT LCDs. Sanyo, for example, produces a 16 inch (40 cm) diagonal black and white LCD. In the United States, UCE Inc. claims the ability to fabricate 1.4 meter diagonal passive STN LCDs, and is seeking to construct an advanced driving system to address and create images on such large LCDs.
Major difficulties remain with the reliable manufacturing of high resolution, high quality TFT LCD plates with up to several million pixels, however. Various technologies are being developed to cope with the production problem. One solution has been to develop alternate technologies which can reduce the electronic complexity of the LCD. For example, the Sarnoff Research Institute recently demonstrated an LCD in which the pixel scanning electronics are integrated onto the glass plate along with the pixel transistors.
A subclass of this approach has been the development of field sequential color techniques that allow each pixel to do the work of three. This could avoid some of the difficulties associated with the manufacture of high resolution LCDs by using fewer pixels. When using a field sequential illumination scheme, a very fast black and white LCD is operated at 180 frames per second. Red, green, and blue lamps (such as strobe fluorescent lamps) are flashed sequentially behind the LCD. Before each color is flashed, the LCD is addressed and made to display the red, green, or blue component of the image, yielding one complete color image every 1/60th second. Since the eye cannot detect image changes at this speed, the observer perceives a nearly flickerless full-color image.
The generation of color images through field sequential color illumination, along with apparatus used to perform this function, is described in several patents, including US-A-4,843,381 (OIS), US-A-4,786,146 (Hughes Aircraft), US-A-5,036,385 (Eichenlaub) and US-A-5,040,878 (Eichenlaub).
The Sarnoff Research Institute and several other companies are actively developing direct view and projection displays based on this method. Since it is relatively easy to create an LCD with many times the normal operating speeds of 60 frames per second (fps), this technique holds great promise. If this technology were combined with present state-of-the-art mass production techniques, color LCDs with resolutions in excess of 3,000,000 pixels could be manufactured.
US-A-5,036,385 describes a method whereby the resolution of a fast liquid crystal display can be increased beyond the total number of pixels on the display by sequentially focusing strobed light into sub regions of each pixel, while the LCD changes the state of the pixels to create intensity levels appropriate to the subregion locations on a high resolution image composed of the subregions, instead of the pixels themselves. Furthermore, the light focused into each subregion can be of different colors, and red, green, and blue light can be sequentially and repeatedly focused into different subregions to create color images composed of red, green, and blue color components.
Previous field sequential color devices have been unusable for many applications because of a phenomena called image breakup. If the user rapidly shifts his or her gaze, or is using a display in an environment where vibrations occur, such as in an aircraft, the red, green, and blue image components tend to be focused on different areas of the retina, resulting in an image that becomes broken up into rapidly shifting red, green, and blue components, particularly around edges. This can make the information on the display unrecognizable. As a result of this phenomena, field sequential color illumination systems have not been accepted in many potential applications areas.
Thus, a need exists for a field sequential color illumination device that will allow full color display without color filters and excessive numbers of pixels, and also will not produce significant image breakup phenomena.